CN116880010B - Integrated annular Bragg metal grating coupler based on lithium niobate and preparation method thereof - Google Patents
Integrated annular Bragg metal grating coupler based on lithium niobate and preparation method thereof Download PDFInfo
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- CN116880010B CN116880010B CN202311143878.6A CN202311143878A CN116880010B CN 116880010 B CN116880010 B CN 116880010B CN 202311143878 A CN202311143878 A CN 202311143878A CN 116880010 B CN116880010 B CN 116880010B
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- GQYHUHYESMUTHG-UHFFFAOYSA-N lithium niobate Chemical compound [Li+].[O-][Nb](=O)=O GQYHUHYESMUTHG-UHFFFAOYSA-N 0.000 title claims abstract description 115
- 229910052751 metal Inorganic materials 0.000 title claims abstract description 91
- 239000002184 metal Substances 0.000 title claims abstract description 91
- 238000002360 preparation method Methods 0.000 title abstract description 12
- 230000008878 coupling Effects 0.000 claims abstract description 62
- 238000010168 coupling process Methods 0.000 claims abstract description 62
- 238000005859 coupling reaction Methods 0.000 claims abstract description 62
- 239000013307 optical fiber Substances 0.000 claims abstract description 35
- 239000000758 substrate Substances 0.000 claims abstract description 26
- 238000004519 manufacturing process Methods 0.000 claims abstract description 25
- VYPSYNLAJGMNEJ-UHFFFAOYSA-N Silicium dioxide Chemical group O=[Si]=O VYPSYNLAJGMNEJ-UHFFFAOYSA-N 0.000 claims description 14
- 239000000463 material Substances 0.000 claims description 11
- 239000010409 thin film Substances 0.000 claims description 10
- 239000010931 gold Substances 0.000 claims description 5
- 239000010408 film Substances 0.000 claims description 4
- 229910052814 silicon oxide Inorganic materials 0.000 claims description 4
- PCHJSUWPFVWCPO-UHFFFAOYSA-N gold Chemical group [Au] PCHJSUWPFVWCPO-UHFFFAOYSA-N 0.000 claims description 3
- 229910052737 gold Inorganic materials 0.000 claims description 3
- 230000000737 periodic effect Effects 0.000 claims 1
- 238000005457 optimization Methods 0.000 abstract description 5
- XUIMIQQOPSSXEZ-UHFFFAOYSA-N Silicon Chemical compound [Si] XUIMIQQOPSSXEZ-UHFFFAOYSA-N 0.000 description 7
- 229910052710 silicon Inorganic materials 0.000 description 7
- 239000010703 silicon Substances 0.000 description 7
- 238000000034 method Methods 0.000 description 5
- 235000012239 silicon dioxide Nutrition 0.000 description 5
- 239000000377 silicon dioxide Substances 0.000 description 5
- 238000010586 diagram Methods 0.000 description 4
- 238000005530 etching Methods 0.000 description 4
- QVGXLLKOCUKJST-UHFFFAOYSA-N atomic oxygen Chemical compound [O] QVGXLLKOCUKJST-UHFFFAOYSA-N 0.000 description 3
- 230000009286 beneficial effect Effects 0.000 description 3
- 229910052681 coesite Inorganic materials 0.000 description 3
- 229910052906 cristobalite Inorganic materials 0.000 description 3
- 229910052760 oxygen Inorganic materials 0.000 description 3
- 239000001301 oxygen Substances 0.000 description 3
- 229910052682 stishovite Inorganic materials 0.000 description 3
- 229910052905 tridymite Inorganic materials 0.000 description 3
- 239000012212 insulator Substances 0.000 description 2
- 230000010354 integration Effects 0.000 description 2
- 238000004088 simulation Methods 0.000 description 2
- 238000007792 addition Methods 0.000 description 1
- 230000005540 biological transmission Effects 0.000 description 1
- 239000000835 fiber Substances 0.000 description 1
- 230000003287 optical effect Effects 0.000 description 1
- 238000006467 substitution reaction Methods 0.000 description 1
Classifications
-
- G—PHYSICS
- G02—OPTICS
- G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
- G02B6/00—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings
- G02B6/10—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings of the optical waveguide type
- G02B6/12—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings of the optical waveguide type of the integrated circuit kind
- G02B6/122—Basic optical elements, e.g. light-guiding paths
- G02B6/124—Geodesic lenses or integrated gratings
-
- G—PHYSICS
- G02—OPTICS
- G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
- G02B6/00—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings
- G02B6/10—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings of the optical waveguide type
- G02B6/12—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings of the optical waveguide type of the integrated circuit kind
- G02B6/13—Integrated optical circuits characterised by the manufacturing method
-
- G—PHYSICS
- G02—OPTICS
- G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
- G02B6/00—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings
- G02B6/10—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings of the optical waveguide type
- G02B6/12—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings of the optical waveguide type of the integrated circuit kind
- G02B2006/12035—Materials
- G02B2006/1204—Lithium niobate (LiNbO3)
-
- G—PHYSICS
- G02—OPTICS
- G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
- G02B6/00—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings
- G02B6/10—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings of the optical waveguide type
- G02B6/12—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings of the optical waveguide type of the integrated circuit kind
- G02B2006/12083—Constructional arrangements
- G02B2006/12107—Grating
-
- G—PHYSICS
- G02—OPTICS
- G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
- G02B6/00—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings
- G02B6/10—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings of the optical waveguide type
- G02B6/12—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings of the optical waveguide type of the integrated circuit kind
- G02B2006/12133—Functions
- G02B2006/12147—Coupler
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- Physics & Mathematics (AREA)
- Engineering & Computer Science (AREA)
- Microelectronics & Electronic Packaging (AREA)
- General Physics & Mathematics (AREA)
- Optics & Photonics (AREA)
- Optical Integrated Circuits (AREA)
Abstract
The invention discloses an integrated annular Bragg metal grating coupler based on lithium niobate and a preparation method thereof, wherein the integrated annular Bragg metal grating coupler comprises a substrate layer, a lithium niobate limiting layer, a lithium niobate waveguide layer, an annular Bragg metal grating layer and an optical fiber; the lithium niobate limiting layer is arranged on the surface of the substrate layer; the lithium niobate waveguide layer is arranged on the surface of the lithium niobate limiting layer and comprises an input straight waveguide, a conical waveguide and a coupling waveguide, wherein one end of the input straight waveguide is connected with the narrow end of the conical waveguide in equal width, and the wide end of the conical waveguide is connected with one end of the coupling waveguide in equal width; the annular Bragg metal grating layer is arranged on the coupling waveguide; the optical fiber is positioned above the annular Bragg metal grating layer and is not in direct contact with the annular Bragg metal grating layer. The invention has the unique advantages of simple manufacturing process, independent flow, high coupling efficiency, mass production and cost optimization, and the like, and can be widely applied to integrated devices and systems on lithium niobate sheets.
Description
Technical Field
The invention belongs to the technical field of integrated optics, and particularly relates to an integrated annular Bragg metal grating coupler based on lithium niobate and a preparation method thereof.
Background
At present, two coupling gratings are mainly used on a lithium niobate integration platform, one is similar to a silicon-based integration platform, and a periodically etched waveguide grating is adopted, but because the refractive index of lithium niobate is far lower than that of silicon, the waveguide grating needs to adopt deep etching with high aspect ratio to realize higher coupling efficiency; the other is to manufacture a silicon-based coupling grating on the top of the lithium niobate waveguide, the structure of the silicon-based coupling grating is unstable, and the etching process of the silicon-based coupling grating may affect the lithium niobate waveguide. The manufacturing process of the two grating couplers based on lithium niobate is complex, the manufacturing process is not independent, the number of steps of interference exposure and surface etching is increased, the manufacturing of the original lithium niobate device is influenced, and the mass production and cost optimization of the preparation of the coupling grating are limited.
Patent document CN111965761a discloses a grating coupler based on a lithium niobate thin film material and a manufacturing method thereof, comprising: a grating coupler based on a lithium niobate thin film material, comprising: the lithium niobate photonic chip on the insulator and the optical fiber arranged above the lithium niobate photonic chip on the insulator sequentially comprise: the device comprises a convergent grating coupling mechanism, a silicon dioxide buried layer and a silicon substrate. The material of the grating coupler disclosed in the patent application is a combination of film lithium niobate and silicon dioxide, the structure is a convergent grating with uniform period, the grating period is 1 mu m, the duty ratio is 0.6, and the coupling efficiency at the 1550nm optical wavelength is lower; and the manufacturing processes of the lithium niobate waveguide and the grating coupler are not independent, and can mutually influence, so that the lithium niobate waveguide and the grating coupler are unstable and are not beneficial to mass production.
Patent document CN113534342a discloses a non-uniform grating coupler of high coupling efficiency based on a lithium niobate thin film waveguide, comprising: a photonic chip on an insulating lithium niobate film and an optical fiber disposed thereon. The photonic chip on the insulating lithium niobate film sequentially comprises from top to bottom: the device comprises a waveguide coupling grating, a lithium niobate thin film layer, a SiO2 oxygen burying layer, an Au reflecting layer and an LN substrate. The grating coupler disclosed in the patent application is composed of three bar gratings with uniform periods and different periods, and is complex in structure; and the Au reflecting layer is arranged below the SiO2 oxygen burying layer, so that the grating coupler has a more complex manufacturing process and is not beneficial to mass production and cost optimization, unlike a structure of a Si substrate of a common lithium niobate photon chip, namely, the SiO2 oxygen burying layer and a lithium niobate thin film layer.
Disclosure of Invention
In view of the above, the invention aims to provide an integrated annular Bragg metal grating coupler based on lithium niobate and a preparation method thereof, wherein the preparation process is simple, the flow is independent, and the coupling efficiency is high.
In order to achieve the above object, an embodiment provides a lithium niobate-based integrated annular bragg metal grating coupler, which includes a substrate layer, a lithium niobate confinement layer, a lithium niobate waveguide layer, an annular bragg metal grating layer, and an optical fiber;
the lithium niobate limiting layer is arranged on the surface of the substrate layer;
the lithium niobate waveguide layer is arranged on the surface of the lithium niobate limiting layer and comprises an input straight waveguide, a conical waveguide and a coupling waveguide, wherein one end of the input straight waveguide is connected with the narrow end of the conical waveguide in equal width, and the wide end of the conical waveguide is connected with one end of the coupling waveguide in equal width;
the annular Bragg metal grating layer is arranged on the coupling waveguide;
the optical fiber is positioned above the annular Bragg metal grating layer and is not in direct contact with the annular Bragg metal grating layer.
In one embodiment, the substrate layer is made of silicon oxide, and the thickness of the substrate layer is not less than 2 μm.
In one embodiment, the lithium niobate confinement layer is made of thin film lithium niobate and has a thickness of 0 μm to 1 μm.
In one embodiment, the material of the lithium niobate waveguide layer is thin film lithium niobate, and the thickness is 0.1 μm-1 μm.
In one embodiment, the width of the input straight waveguide is 0.1 μm-5 μm, the width of the coupling waveguide is 0.1 μm-20 μm, the length of the tapered waveguide is 0.1 μm-10 μm, and the width of the input straight waveguide is smaller than the width of the coupling waveguide.
In one embodiment, the material of the annular Bragg metal grating layer is gold, and the thickness is 0.01 μm-1 μm.
In one embodiment, the annular Bragg metal grating layer is an annular Bragg grating structure with a plurality of grating teeth unevenly and periodically arranged.
In one embodiment, the annular bragg grating structure has a plurality of grating teeth which are circular arcs with the same angle, the same circle center and different radii, the angles are all 10-180 degrees, the widths of the grating teeth are 0.01-1 μm, the number of the grating teeth is at least 2, and the distance between every two adjacent grating teeth is 0.01-1 μm.
In one embodiment, for a non-uniform periodically arranged ring-shaped bragg grating structure, if the number of grating teeth is less than four, then the widths of all grating teeth and the distances between adjacent grating teeth are all different; if the number of grating teeth is greater than four, the widths of the first four grating teeth and the distances between the first four grating teeth and the respective next grating teeth are different, the widths of all the remaining grating teeth are the same, and the distances between all the remaining adjacent grating teeth are the same.
In one embodiment, the optical fiber has an air gap distance of 0.01 μm to 10 μm from the annular Bragg metal grating layer, and the axis of the optical fiber is at an angle of 0 ° to 10 ° from the surface normal of the annular Bragg metal grating layer.
In order to achieve the above object, the embodiment of the present invention further provides a method for manufacturing the integrated annular bragg metal grating coupler based on lithium niobate, including the following steps:
step 1, preparing a substrate layer;
step 2, preparing a lithium niobate limiting layer on the substrate layer;
step 3, preparing a lithium niobate waveguide layer on the lithium niobate limiting layer;
step 4, preparing an annular Bragg metal grating layer on the lithium niobate waveguide layer;
and 5, arranging optical fibers on the annular Bragg metal grating layer to obtain the integrated annular Bragg metal grating coupler.
Compared with the prior art, the invention has the beneficial effects that at least the following steps are included:
according to the integrated annular Bragg metal grating coupler based on lithium niobate and the preparation method thereof, the annular Bragg grating structure which is unevenly and periodically arranged is utilized, and the vertical diffraction of light can be effectively realized by adjusting the distance between different grating teeth, so that the coupling efficiency is high and the coupling bandwidth is large; the manufacturing process is simple, the flow is independent, no influence is generated on the manufacturing of the original lithium niobate device, the method has unique advantages in the aspects of mass production, cost optimization and the like, and the method can be widely applied to integrated devices and systems on lithium niobate sheets.
Drawings
In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings that are required in the embodiments or the description of the prior art will be briefly described, and it is obvious that the drawings in the following description are only some embodiments of the present invention, and other drawings may be obtained according to these drawings without inventive effort for a person skilled in the art.
Fig. 1 is a schematic side view structural layered diagram of an integrated annular bragg metal grating coupler based on lithium niobate according to an embodiment of the present invention;
fig. 2 is a schematic top view of an integrated ring-shaped bragg metal grating coupler based on lithium niobate according to an embodiment of the present invention;
FIG. 3 is a schematic diagram of transmission line simulation results of an integrated annular Bragg metal grating coupler based on lithium niobate according to an embodiment of the present invention;
fig. 4 is a flowchart of a preparation method of an integrated annular bragg metal grating coupler based on lithium niobate according to an embodiment of the present invention.
Detailed Description
The present invention will be described in further detail with reference to the drawings and examples, in order to make the objects, technical solutions and advantages of the present invention more apparent. It should be understood that the detailed description is presented by way of example only and is not intended to limit the scope of the invention.
The invention is characterized in that: in order to solve the technical problems that in the existing coupling grating, the manufacturing process is complex, the manufacturing process is not independent, the number of steps of interference exposure and surface etching is increased, the manufacturing of the original lithium niobate device is influenced, the mass production of the coupling grating preparation is limited, and the cost optimization is realized, the embodiment of the invention provides the integrated annular Bragg metal grating coupler based on lithium niobate and the manufacturing method.
Fig. 1 is a schematic diagram of a side view structure layering of an integrated annular bragg metal grating coupler based on lithium niobate provided in the embodiment, as shown in fig. 1, where the integrated annular bragg metal grating coupler based on lithium niobate provided in the embodiment 1 includes a substrate layer 1, a lithium niobate confinement layer 2, a lithium niobate waveguide layer 3, an annular bragg metal grating layer 4, and an optical fiber 5, where the lithium niobate confinement layer 2 is disposed on the substrate layer 1, the lithium niobate waveguide layer 3 is disposed on the lithium niobate confinement layer 2, and the optical fiber 5 is disposed above the annular bragg metal grating layer 4 and does not directly contact the annular bragg metal grating layer 4.
In an embodiment, the material of the substrate layer 1 may be silicon oxide or a combination of silicon oxide and silicon, and the thickness of the substrate layer 1 may be not less than 2 μm. By providing a sufficient thickness of the substrate layer 1, it is possible to provide sufficient support for the lithium niobate confinement layer 2, the lithium niobate waveguide layer 3, and the annular bragg metal grating layer 4, ensuring process realization of the lithium niobate waveguide and the annular bragg metal grating.
In the embodiment, the material of the lithium niobate confinement layer 2 may be thin film lithium niobate, the thickness of the lithium niobate confinement layer 2 may be set to a thickness between 0 μm and 1 μm, and further preferably, the thickness of the lithium niobate confinement layer 2 may be set to 0.3 μm and 0.4 μm, when the thickness of the lithium niobate confinement layer 2 is set to 0 μm, it is indicated that the lithium niobate confinement layer 2 may not be provided, and by setting a suitable thickness of the lithium niobate confinement layer 2, light can be ensured to be transmitted in the lithium niobate waveguide layer 3.
In an embodiment, the material of the lithium niobate waveguide layer 3 may be thin film lithium niobate, and the thickness of the lithium niobate waveguide layer 3 may be set to a thickness between 0.1 μm and 1 μm. Further preferably, the thickness of the lithium niobate waveguide layer 3 may be set to 0.3 μm to 0.4 μm, and the lithium niobate waveguide layer 3 further includes an input straight waveguide 301, a tapered waveguide 302, and a coupling waveguide 303, wherein one end of the input straight waveguide 301 is connected to a narrow end of the tapered waveguide 302 in equal width, and a wide end of the tapered waveguide 302 is connected to one end of the coupling waveguide 303 in equal width. The thickness of the lithium niobate waveguide layer 3 is equal to the thicknesses of the input straight waveguide 301, the tapered waveguide 302, and the coupling waveguide 303. By setting a suitable thickness of the lithium niobate waveguide layer 3, it is ensured that light can be transmitted in the lithium niobate waveguide layer 3.
As further shown in fig. 1, a ring-shaped bragg metal grating layer 4 is disposed on the coupling waveguide 303 of the lithium niobate waveguide layer 3. The annular Bragg metal grating layer 4, the input straight waveguide 301, the conical waveguide 302 and the coupling waveguide 303 are arranged on different layers, so that the manufacturing flow of the annular Bragg metal grating layer 4 is independent, and the influence of the technical manufacturing process of the grating on the technical manufacturing of the lithium niobate waveguide is avoided.
Continuing to show in fig. 1, the optical fiber 5 is located directly above the annular bragg metal grating layer 4 and is not in direct contact; the air gap distance between the optical fiber 5 and the bragg metal grating layer 4 may be one thickness of between 0.01 μm and 10 μm, and further preferably, the air gap distance may be 1 μm to 3 μm; the angle between the axis of the optical fiber 5 and the surface normal of the annular bragg metal grating layer 4 may be a value between 0 degrees and 10 degrees, and further preferably the angle may be 4.5 degrees and 5.5 degrees. By setting the appropriate air gap distance between the optical fiber 5 and the annular bragg metal grating layer 4 and the appropriate angle between the axis of the optical fiber 5 and the surface normal of the annular bragg metal grating layer 4, it is possible to maximally ensure that light can be smoothly coupled from the annular bragg metal grating layer 4 into the optical fiber 5, and also to maximally ensure that light can be smoothly coupled from the optical fiber 5 into the annular bragg metal grating layer 4.
In an embodiment, the material of the ring-shaped bragg metal grating layer 4 may be gold, and the thickness of the ring-shaped bragg metal grating layer 4 may be one thickness between 0.01 μm and 1 μm, and further preferably, the thickness of the ring-shaped bragg metal grating layer 4 may be 0.12 μm and 0.14 μm. By setting a suitable thickness of the annular bragg metal grating layer 4, a vertical diffraction of the light transmitted in the coupling waveguide 303 can be achieved, thereby enabling coupling of the light transmitted in the coupling waveguide 303 into the optical fiber 5 or coupling of the light transmitted in the optical fiber 5 into the coupling waveguide 303.
Fig. 2 shows a schematic top view structure of an integrated annular bragg metal grating coupler based on lithium niobate according to an embodiment of the present invention. As shown in FIG. 2, the input straight waveguide 301 may have a width between 0.1 μm and 5 μm, the coupling waveguide 303 may have a width between 0.1 μm and 20 μm, and the tapered waveguide 302 may have a length between 0.1 μm and 10 μm. By setting the appropriate width of the input straight waveguide 301 and the width of the coupling waveguide 303, it is ensured that light can be transmitted in the input straight waveguide 301 and the coupling waveguide 303, respectively. The width of the input straight waveguide 301 is smaller than the width of the coupling waveguide 303, the width of the narrow end of the tapered waveguide 302 is equal to the width of the input straight waveguide 301, and the width of the wide end of the tapered waveguide 302 is equal to the width of the coupling waveguide 303. Further preferably, the width of the input straight waveguide 301 may be 1.5 μm to 2.5 μm, the width of the coupling waveguide 303 may be 11 μm to 13 μm, and the length of the tapered waveguide 302 may be 0.2 μm to 0.4 μm. By setting the length of the tapered waveguide 302 appropriately, light transmitted in the coupling waveguide 303 can be transmitted through the tapered waveguide 302 into the input straight waveguide 301 with extremely low loss, and light transmitted in the input straight waveguide 301 can also be transmitted through the tapered waveguide 302 into the coupling waveguide 303 with extremely low loss.
It should be noted that the widths of the ring-shaped bragg metal grating layers 4 and 303 are not necessarily equal, and the relationship between the two is that the width of the ring-shaped bragg metal grating layer 4 is necessarily smaller than or equal to the width of 303, and the length of the ring-shaped bragg metal grating layer 4 and 303 is not necessarily equal, and the relationship between the two is that the length of the ring-shaped bragg metal grating layer 4 is necessarily smaller than or equal to the length of 303, and the length of the ring-shaped bragg metal grating layer 4 is not greater than the length of 303.
With continued reference to fig. 2, the annular bragg metal grating layer 4 includes a plurality of grating teeth 401, which may be non-uniformly periodically arranged annular bragg grating structures. The grating teeth 401 have the same angle, the same center of circle and different radii. The angle of grating teeth 401 may be a value in the middle of 10-180 degrees. The grating teeth 401 may be circular arcs and the width of the grating teeth 401 may be a value in the middle of 0.01 μm-1 μm. The number of grating teeth 401 may be a number greater than 2. The distance between two adjacent grating teeth 401 may be a length between 0.01 μm and 1 μm. Further preferably, the angle of the grating teeth 401 may be 15 degrees to 25 degrees, the width of the grating teeth 401 may be 0.05 μm to 0.5 μm, the distance between two adjacent grating teeth 401 may be 0.01 μm to 0.7 μm, and the number of grating teeth may be 22 to 24. By setting the angle and width of the grating teeth 401 and the number of grating teeth 401 and the distance between adjacent grating teeth 401, it is ensured that the annular bragg metal grating layer 4 can achieve a higher coupling efficiency and a wider coupling bandwidth.
Specifically, in the non-uniform periodically arranged ring-shaped bragg grating structure, if the number of grating teeth is less than four, the widths of all grating teeth and the distances between adjacent grating teeth are different; if the number of grating teeth is greater than four, the widths of the first four grating teeth and the distances between the first four grating teeth and the respective next grating teeth are different, the widths of all the remaining grating teeth are the same, and the distances between all the remaining adjacent grating teeth are the same.
The working principle of the integrated annular Bragg metal grating coupler based on lithium niobate provided by the embodiment is as follows: the transmitted light inputted into the straight waveguide 301 passes through the tapered waveguide 302 to enter the coupling waveguide 303 with extremely low loss; light transmitted in the coupling waveguide 303 is vertically diffracted as it passes through the annular bragg metal grating layer 4, and a portion of the light is diffracted upward and then coupled into the optical fiber 5; a part of the light is diffracted downwards, which will be reflected at the interface between the lithium niobate confining layer 2 and the substrate layer 1, i.e. the interface where the refractive index changes, and then a part of the light diffracted downwards will be diffracted upwards again into the optical fiber 5. Conversely, the light transmitted in the optical fiber 5 is also diffracted vertically when passing through the ring-shaped bragg metal grating layer 4, and a part of the light is diffracted to the left, transmitted in the coupling waveguide 303, and then transmitted into the input straight waveguide 301 through the tapered waveguide 302; a portion of the light is diffracted to the right, reflected to the left upon contact with the interface between the lithium niobate confining layer 2 and the substrate layer 1, and coupled into the input straight waveguide 303. The embodiment of the invention adopts a ring-shaped Bragg metal grating structure with non-uniform period, so that more light can be diffracted upwards (when light enters from the input straight waveguide 301) or diffracted leftwards (when light enters from the optical fiber 5), and higher coupling efficiency can be obtained.
Fig. 3 is a schematic diagram of simulation results of coupling efficiency of an integrated annular bragg metal grating coupler based on lithium niobate according to an embodiment of the present invention. In this embodiment, the thickness of the substrate layer 1 is 3 μm, the thickness of the lithium niobate confining layer 2 is 0.3 μm, the thickness of the lithium niobate waveguide layer 3 is 0.3 μm, the thickness of the annular Bragg metal grating layer 4 is 0.13 μm, and the optical fiber 5 is a common single mode fiber. The air gap distance between the optical fiber 5 and the annular bragg metal grating layer 4 is 2 μm, and the angle between the axis of the optical fiber 5 and the surface normal of the annular bragg metal grating layer 4 is 4.9 degrees. The width of the input straight waveguide 301 is 2 μm, the width of the coupling waveguide 303 is 12 μm, and the length of the tapered waveguide 302 is 0.3 μm. The annular Bragg metal grating layer 4 comprises 23 grating teeth 401, the centers of the 23 grating teeth 401 are the same, and the angles are 20 degrees. The first 4 grating teeth 401 of the 23 grating teeth 401 have widths of 0.18 μm, 0.07 μm, 0.21 μm, and 0.33 μm, respectively, and the last 19 grating teeth 401 have widths of 0.47 μm. The distances between the first 4 grating teeth 401 of the 23 grating teeth 401 and the next grating tooth 401 are 0.02 μm, 0.63 μm, 0.51 μm and 0.37 μm, and the distances between the last 18 grating teeth and the next grating tooth 401 are 0.36 μm. Note that, the abscissa of fig. 3 is the wavelength of light, and the unit is nm; the ordinate of fig. 3 is the coupling efficiency in%. The coupling efficiency may be defined as the ratio of the light intensity transmitted in the optical fiber 5 to the light intensity transmitted in the input straight waveguide 301. The coupling bandwidth may be defined as a range of wavelengths of light for which the coupling efficiency is greater than 50%. In this embodiment, light enters from the optical fiber 5, is coupled into the coupling waveguide 303 through the ring-shaped bragg metal grating layer 4, and is transmitted into the input straight waveguide 301 through the tapered waveguide 302.
As can be seen from fig. 3, the coupling efficiency of the integrated annular bragg metal grating coupler based on lithium niobate provided in this embodiment is equal to 62.8% at a wavelength of 1556.7nm, and can be maintained at 50% or more in a range of 1525.4nm to 1588.4nm up to 63nm, and the coupling bandwidth can be up to 63nm.
Fig. 4 is a flowchart of a preparation method of an integrated annular bragg metal grating coupler based on lithium niobate according to an embodiment of the present invention. As shown in fig. 4, the preparation method of the integrated annular bragg metal grating coupler based on lithium niobate provided in the embodiment includes the following steps:
s410, preparing a substrate layer;
s420, preparing a lithium niobate limiting layer on the substrate layer;
s430, preparing a lithium niobate waveguide layer on the lithium niobate confining layer;
s440, preparing an annular Bragg metal grating layer on the lithium niobate waveguide layer;
s450, arranging optical fibers on the annular Bragg metal grating layer to obtain the integrated annular Bragg metal grating coupler.
The foregoing detailed description of the preferred embodiments and advantages of the invention will be appreciated that the foregoing description is merely illustrative of the presently preferred embodiments of the invention, and that no changes, additions, substitutions and equivalents of those embodiments are intended to be included within the scope of the invention.
Claims (5)
1. The integrated annular Bragg metal grating coupler based on the lithium niobate is characterized by comprising a substrate layer, a lithium niobate limiting layer, a lithium niobate waveguide layer, an annular Bragg metal grating layer and an optical fiber;
the lithium niobate limiting layer is arranged on the surface of the substrate layer, the material of the lithium niobate limiting layer is film lithium niobate, and the thickness is 0-1 mu m;
the lithium niobate waveguide layer is arranged on the surface of the lithium niobate limiting layer and comprises an input straight waveguide, a conical waveguide and a coupling waveguide, wherein one end of the input straight waveguide is connected with the narrow end of the conical waveguide in equal width, the wide end of the conical waveguide is connected with one end of the coupling waveguide in equal width, the lithium niobate waveguide layer is made of thin film lithium niobate, and the thickness of the lithium niobate waveguide layer is 0.1 mu m-1 mu m;
the annular Bragg metal grating layer is arranged on the coupling waveguide, the material of the annular Bragg metal grating layer is gold, the thickness of the annular Bragg metal grating layer is 0.01 mu m-1 mu m, the annular Bragg metal grating layer is an annular Bragg grating structure with a plurality of grating teeth which are unevenly and periodically arranged, in the annular Bragg grating structure, the plurality of grating teeth are circular arcs with the same angle, the same circle center and different radiuses, the angles are 10 degrees-180 degrees, the width of each grating tooth is 0.01 mu m-1 mu m, the number of the grating teeth is at least 2, and the distance between every two adjacent grating teeth is 0.01 mu m-1 mu m;
the optical fiber is positioned above the annular Bragg metal grating layer and is not in direct contact with the annular Bragg metal grating layer;
for the annular Bragg grating structure with non-uniform periodic arrangement, if the number of grating teeth is smaller than four, the widths of all grating teeth and the distances between adjacent grating teeth are different; if the number of grating teeth is greater than four, the widths of the first four grating teeth and the distances between the first four grating teeth and the respective next grating teeth are different, the widths of all the remaining grating teeth are the same, and the distances between all the remaining adjacent grating teeth are the same.
2. The lithium niobate-based integrated annular bragg metal grating coupler of claim 1, wherein said substrate layer is silicon oxide having a thickness of not less than 2 μm.
3. The lithium niobate based integrated ring bragg metal grating coupler of claim 1, wherein said input straight waveguide has a width of 0.1 μm-5 μm, said coupling waveguide has a width of 0.1 μm-20 μm, said tapered waveguide has a length of 0.1 μm-10 μm, and said input straight waveguide has a width less than a width of said coupling waveguide.
4. The lithium niobate based integrated annular bragg metal grating coupler of claim 1, wherein the optical fiber has an air gap distance from the annular bragg metal grating layer of 0.01 μιη -10 μιη, and the axis of the optical fiber has an angle between 0 ° -10 ° with the surface normal of the annular bragg metal grating layer.
5. A method of making a lithium niobate-based integrated annular bragg metal grating coupler according to any of claims 1-4, comprising the steps of:
step 1, preparing a substrate layer;
step 2, preparing a lithium niobate limiting layer on the substrate layer;
step 3, preparing a lithium niobate waveguide layer on the lithium niobate limiting layer;
step 4, preparing an annular Bragg metal grating layer on the lithium niobate waveguide layer;
and 5, arranging optical fibers on the annular Bragg metal grating layer to obtain the integrated annular Bragg metal grating coupler.
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